Keywords: The 2016 Kumamoto Earthquake, Terrestrial laser scanning, Point clouds, High-definition topographical data, Landslides, Time series analysis
The 2016 Kumamoto earthquake triggered many landslides on steep slopes in the Sensuikyo area near the Aso Volcano in Kumamoto, western Japan. In this research, we use the terrestrial laser scanning to obtain detailed point cloud data of the slopes including landslides before and after the earthquake. We analyze the point cloud data regarding the changes in elevation and topographic profiles. It is observed that new landslides were formed by the earthquake on slopes where landslides formed by the heavy rainfall in July 2012 have already been present. The depth of the earthquake-derived landslides is about 6 m, which is deeper than the past landslides caused by heavy rainfalls. We also found that the longitudinal profiles of the earthquake-driven landslides exhibit different shapes from those of the rainfall-triggered landslides: The former is more curved, while the latter is straight. This suggests that the landslides by the earthquake have occurred along a slip surface deeper than that of the rainfall-derived landslides. Also, further decreases in elevation were partially observed on the ridge, the middle part of the slope, and the valley bottom after the earthquake. This suggests that there were further collapses and erosion possibly caused by a relatively heavy rainfall in June 2016.